BUILDING STONES. 181 



Sandstones. ] 



sandrock used in the Milwaukee court house, and a great many brown stone 

 fronts in that city and in Chicago were obtained from it. It was formerly 

 quarried on the south side of Siskiwit bay, on Lsle Royale, and sold in 

 Detroit as Tsle Royale brownstone. While it consists largely of quartz, the 

 grains are not so firmly cemented or united as to render it objectionably 

 hard except when it has been subjected to metamorphic agencies, a in 

 Pipestone county and in some of the analogous knobs seen in the northern 

 part of the state.* On Isle Eoyale, when quarried, it is fine-grained and 

 rather brittle, being more metamorphosed than at Fond du Lac. At some 

 points it has a mottling of red and gray, as at Sault St. Marie, at the eastern 

 end of lake Superior, where the ship canal is cut in it, and largely built 

 of it. At Fond du Lac it has also a mottling of green, particularly at the 

 quarry on Mission creek. In some places it is so loosely cemented as to 

 crumble and to be rendered useless for building, and in others it contains 

 pebbles, and even stones several inches in diameter, of white quartz, or even 

 becomes wholly conglomeritic. Nearly all these features can be seen at 

 Fond du Lac, but there is still at that place a great abundance of fine stone 

 of the best quality. Its strength under pressure is from five to eight thou- 

 sand pounds per square inch, tested for the survey by general Gillmore. 



At Fond du Lac this stone, while in general of a reddish-brown color, 

 is variously marked with spots and stripes of lighter shade. It also has 

 occasional grains of quartz as large as a pea, or even as large as a hen's egg, 

 distributed especially through the lighter colored portions, but not much of 

 it is conglomeritic. Sometimes flattened lumps of red shale from two to five 

 inches across are seen arranged in belts coincident rudely with the strati- 

 fication. The strata are of all thicknesses up to three or four feet, and very 

 large blocks are obtainable. The principal quarry is owned by Mr. M. Boyle. 

 It is situated in the bluff of the St. Louis river a short distance above Fond du 

 Lac, at the first rapids, and was first opened by Mr. M. E. Chambers in 1870. 

 The stone appears, and has been worked, on both sides of the river, but the 

 principal excavation is on the Minnesota side from twenty to forty feet 

 above the water, near the St. Paul and Duluth railroad. It is also opened 

 on Mission creek, north of Fond du Lac, by James G. McDonald, where some 



Tenth annual report, p. 101. Nos. 784, 785. 



